The present invention relates to a new and improved audio amplifier of the type including a plurality of amplifying systems each having a preamplifier and a main amplifier.
With the prevalence of the so-called audio component systems, higher performance has become an important and requisite factor in present day audio systems. In audio amplifiers, a tendency toward increased power is very noticeable, the purpose of which is to improve sound quality in addition to increasing capacity and enhancing stability.
The power source in the audio amplifier generally is not taken seriously since its construction is simple as compared with that of its associated amplifier circuitry. In designing the totality of an audio system, however, the power source is very important since it occupies a considerable part of the total weight and space of the audio system. In designing a power source, a hearing test was conducted by varying the power source voltage to follow the envelope of the musical sound at a low frequency. In the test, it was found that, when a low frequency signal was applied to the amplifier system, the localization of the sound image transiently varied with the power source voltage variation, and when a small signal of high frequency was applied, a noisy sound was produced. From this, the presumption was made that, when a signal was applied to the amplifying system of one of channels in the audio amplifier, power source voltage variation corresponding to the envelope of the input signal takes place in the power source circuit of the audio amplifier. The voltage variation causes the operation points of the amplifying system in other channels to shift, resulting in a transient distortion. This transient distortion does not take place during static operation of an audio amplifier when it receives a continuous wave signal but it is caused by transient variations which occur when the audio amplifier receives a dynamic or transient signal such as a musical sound signal. The distortion is generally called dynamic crosstalk or transient crosstalk. In this specification, it will be referred to as transient crosstalk.
Various attempts have therefore been made with a view to eliminating the transient crosstalk. Examples of such attempts are to stabilize the voltage of the power source circuit and to lower the power source impedance. None of these attempts have, however, been fully successful.